Total temporomandibular joint (TMJ) replacement occurs in the art when the TMJ has become damaged, infected, resorbed, ankylosed or was formed in a defective manner or even haven't formed at all. Each human has two joints that arise from the lower jaw (mandible) and articulates with the skull at the temporal bone. Therefore, this joint is called “the temporomandibular joint” or TMJ. Several muscles are attached simultaneously to the mandible and the skull. Throughout synchronized movements of these muscles (extension or contraction), movement of the mandible is possible, and thus a human is able to open and close his/her mouth.
In the facial skeleton, the temporomandibular joint serves as an important local facial growth center. In people with a healthy and properly functioning temporomandibular joint, this joint is the center in which the lateral side of the face grows in all three dimensions (height, width, and depth). Therefore, any disturbance; trauma; neoplasm; or even congenital abnormality to the joint—and particularly the mandibular condyle—will cause disturbance of the growth to the face.
In conclusion: the TMJ not only provides the normal hinge/sliding movement of the lower jaw, but also serves as a local growth center of the face.
More specifically, describing the anatomy, which is useful in understanding the technology presented herein, there are two TMJs, one on either side of the mandible/face. The name is derived from the two bones which form the joint: the ramus (referred to herein as the “generally vertical” or “vertical portion,” for convenience) and the body of the mandible (referred to herein as the “generally horizontal” or “horizontal portion”. The unique feature of the TMJs is the articular disc. The disc is composed of fibrocartilagenous tissue (like the firm and flexible elastic cartilage of the ear) which is positioned between the two bones that form the joint. The TMJs are one of the few synovial joints in the human body with an articular disc, another being the sternoclavicular joint. The disc divides each joint into two. The lower joint compartment formed by the mandible and the articular disc is involved in rotational movement—this is the initial movement of the jaw when the mouth opens. The upper joint compartment formed by the articular disk and the temporal bone is involved in translational movement—this is the secondary gliding motion of the jaw as it is opened widely. The part of the mandible which mates to the under-surface of the disc is the condyle, and the part of the temporal bone which mates to the upper surface of the disk is the glenoid (or mandibular) fossa.
The surfaces in contact with one another (bone and cartilage) do not have any receptors to transmit the feeling of pain. The pain therefore originates from one of the surrounding soft tissues, from the posterior part of the disc, or from the trigeminal nerve itself, which provides innervations to the joint area. When receptors from one of these areas are triggered, the pain can cause a reflex to limit the mandible's movement. Furthermore, inflammation of the joints or damage to the trigeminal nerve can cause constant pain, even without movement of the jaw.
In the field of cranio/maxillo/facial/re-constructive surgery, an artificial temporomandibular joint device may be used to replace a diseased TMJ which is damaged beyond repair or not biologically/physiologically functioning. Prior art TMJ prosthesis, such as those disclosed at tmjconcepts.com, at the time of this writing, include a metal condyle made from cobalt-chromium-molybdenum, and a metal prosthesis made from a titanium alloy, anchored to the lower jaw with titanium alloy screws. In the prior art, the component attaching to bone (fossa component) “has a durable medical-grade plastic surface made from ultra-high-molecular-weight polyethylene (also known as UHMWPE). This is attached to a metal backing made from pure titanium. This component is anchored to the skull with titanium alloy screws.” Such prior art prosthesis are shaped to fit a particular skull and lower jaw.
Again, as disclosed on tmjconcepts.com, the method of prosthesising is as follows, in the prior art: 1) Computed axial tomography (CAT scan) of the jaw region, 2) construction of an anatomical bone, 3) review by a surgeon, 4) surgical prosthesis placement. With the patient under general anesthesia, and using two incisions, the components are surgically placed—the condylar component is placed through an incision below and behind the lower jaw, and the fossa component is prosthesised through an incision in front of the ear.
The problem with such prosthetic devices, as written on tmjconcepts.com at the time of filing this application, is as follows: “Despite the fact that these implants are fitted specifically to your anatomy, you should not expect them to last for a lifetime. While the expected life of a TMJ implant is difficult to estimate, it is finite and may significantly differ for each patient due to the diversity of conditions seen in TMJ reconstruction.” Thus, the problem known in the art is that the implants are fitted for a particular person, with a particular size. This is especially problematic in the case of a growing person (a child), one healing from an accident (whose anatomy is likely to change), and the like. The shape and size of a person is bound to change slowly over time, while the prosthesis will not. This causes the person's face to be uneven, or worse, and will necessitate another surgical procedure to replace the prosthetic device, including removing the first prosthesis, and screws through the bone, and placing a new prosthesis with new fixation points. This is, obviously, undesirable because it requires additional invasive surgical procedures, increases the risk of failure, and decreases mouth opening ability due to increased scarring of the area. As the patient is required to undergo additional surgical procedures, this also increases costs and recovery time.
It is therefore an object of the disclosed technology to provide a TMJ surgical prosthesis which is more versatile than the prior art, and which may remain in place, despite changes in the anatomy of a person receiving the prosthesis.